Ozone can be used in various semiconductor processing systems. For example, ozone can be used in the formation of insulating layers on semiconductor wafers by growing insulating films or by oxidizing thin films on the wafer. Ozone can be used for surface conditioning of a semiconductor wafer prior to deposition of device elements. Another application for ozone in semiconductor processing is for cleaning semiconductor wafers and the processing chambers of semiconductor equipment. Ozone is particularly useful for removing hydrocarbons from the surface of semiconductor wafers or from processing chambers.
The use of ozone in semiconductor processing has imposed increased demands on ozone generating equipment. For semiconductor processing applications, ozone, as well as other gases delivered to a processing chamber, must be very pure so that the delivered gas does not introduce contaminants into the process. Some ozone generators require the use of inert dopant gases, such as for example, nitrogen or carbon dioxide, to increase the ozone concentration to acceptable levels.
In general, to increase productivity, a semiconductor processing tool can utilize multiple chambers. While it would be advantageous to use a single ozone generator to feed ozone to more than one chamber of a tool to decrease equipment and operating costs, conventional systems use a dedicated ozone generator for each processing chamber due to difficulties that arise during initiation or discontinuation of a chamber. For example, large increases or decreases from a desired concentration level in semiconductor processing over a time interval of 20 seconds or greater can have disastrous effects on semiconductor device quality. When one ozone generator is used to service multiple chambers, the conventional control systems in general have a reaction or settling time of 30 seconds or greater. See, for example, FIG. 1, showing a typical response time for a PID controller, wherein the settling time is about 70 seconds to achieve a desired 300 g/m3 concentration for a 10 slm flow rate. As a result, concentration levels in the chambers during the 30-second settling time differ from the desired level, thereby leading to a compromised semiconductor product.